The Overlooked Sub-Grid Air-Sea Flux in Climate Models

Understanding air-sea interaction is crucial for our ability to predict future states of the climate system, and to inform economic and societal decision-making. However, the representation of air-sea interactions in climate models is limited by structural errors associated with model resolution. Coarse-resolution climate models do not resolve small-scale structures in the air-sea state, which, due to strong nonlinearities in the coupling formulae, can impact the large-scale air-sea exchange—a mechanism that has received little attention and is the focus of this paper. Since observations at the temporal and spatial coverage needed to study this problem do not yet exist, we quantify the impact of this small-scale heterogeneity on the large-scale air-sea heat flux by analyzing 1/10° coupled climate simulations. This effect systematically cools the ocean by about 4W/m2 globally—with large spatio-temporal variations—and mostly enhances the large-scale heat flux. By identifying an overlooked contribution to air-sea heat flux in climate models, we open a promising new direction for addressing biases in climate simulations and thus improving future climate predictions. Furthermore, future observations, like the newly proposed satellite mission ODYSEA35, could potentially observe and quantify this effect directly.